1. Field of the Invention
The invention concerns a force transducer in the form of a double tuning fork adapted to vibrate at an intrinsic frequency which is representative of the amplitude of a longitudinal force applied to it, a manufacturing process for a transducer of this kind and an application of this transducer within a load cell, for use in a weighing instrument, for example.
2. The Prior Art
Double tuning fork force transducers are already known, in particular from the documents U.S. Pat. No. 4,299,122 (Y.E.W.) and DE No. 3.423.501 (SHINKO DENSHI). A notable benefit of these transducers is that, because the branches of the double tuning fork vibrate in phase opposition, vibrational energy losses are limited. These transducers are equipped with an excitation device and a frequency sensor. They may be fitted into load cells but also, and particularly, into pressure sensors.
Although the document U.S. Pat. No. 4,299,122 mentions the possibility of manufacturing a transducer of this kind in several parts, this document and the previously mentioned German document describe transducers of unitary construction.
In practice, currently known transducers are cut out from the solid by wire electro-erosion, which is slow and costly. For example, electro-erosion of "ELINVAR" blocks proceeds at the rate of approximately 2 mm/min. Also, the system controlling the path of the cutting wire is generally complex and costly.
As the intrinsic frequencies of these transducers are likely to vary not only with the applied force but also with the length of their branches, the materials used are generally chosen to have negligible coefficients of expansion.